The field of the invention is sputtering and the apparatus which is used in sputtering techniques. Specifically the invention is concerned with sputtering machines in which the anode is rotary and a flexible substrate is led over the anode and required to receive materials that are deposited thereon.
Generally the apparatus which comprises the environment of the invention and the method of sputtering are both disclosed in U.S. Pat. No. 3,884,787. The structure which is disclosed in said patent and which is common to the structure of the invention herein includes a pressure vessel having at least one target or cathode mounted therein, a rotary anode mounted for rotation within the vessel, means for mounting a supply of flexible substrate such as polyester film in the vessel, means for mounting a take-up mechanism in the vessel, and suitable controls for operating the apparatus. The substrate is arranged to be led over the anode and a sputtering plasma established in the vessel. The material from which the target is made is sputtered onto the anode, but since the substrate is carried on the surface of the anode, the material is coated onto the substrate.
It is understood that auxiliary apparatus, supply means and controls are provided for furnishing the ionizing gas and its mixed components and for monitoring and controlling the feed to the chamber; for furnishing electrical energy to the apparatus and monitoring and controlling the same and its effects; for controlling and monitoring speed, temperature, thickness of deposit, and many other parameters; for driving the substrate in its path and monitoring and controlling its tension; etc.
In a technique which has been studied and developed, it has been found that for the deposit of certain materials, particularly photoconductors upon thin, flexible, transparent substrates, the conditions of deposition include, among others, the following:
a. The anode is required to rotate,
b. The power which is supplied is coupled to the cathode, anode and shielding in the vessel in an electrical circuit or network in which the cathode is at maximum negative voltage, the shielding is at ground potential and the anode is at a potential that is also negative with respect to ground, but to a much lesser degree than the cathode,
c. The anode surface is required to be temperature controlled to prevent excessive loss of heat during sputtering,
Certain other requirements of the apparatus render the achievement of the above conditions very difficult to effect and these include:
d. Maintaining all of the supporting structure of the apparatus including the chamber walls, at ground potential for practicality and safety,
e. Maintaining the ends of the drum shielded to prevent excessive deposit thereon,
f. Moving the substrate-carrying portion or transport of the apparatus into and out of the chamber when the sputtering is completed.
The last-mentioned requirement is for the most part understood to be necessary from the above-mentioned patent in the case of a sputtering apparatus which is to produce quantities of sputtered substrate and which of necessity is large and cumbersome. The solution to the problem proposed by the patent is to mount the substrate-carrying portion of the apparatus on a carriage along with much of the control and measuring equipment and to fix the chamber and all of its auxiliary apparatus to a support which is stationary. In such case the targets are secured within the chamber and the high voltage connections are associated with the chamber, along with the controls and instrumentation therefor; however, this arrangement does not take into consideration that the anode must be maintained at a voltage different from ground.
The invention herein provides a solution to all of the problems which are raised by the above conditions in an unobvious manner by means which are elegant and yet simple and economical.